Silicon powder may be generated during the manufacture of crystalline solar cells as wire saws or band saws are used to trim the dimensions of a multicrystalline or monocrystalline ingot. In addition, silicon powder may be created during the cutting of silicon blocks or boules into wafers by wire saws, such as during the semiconductor wafer manufacturing process. Grinding or crushing processes may also create silicon powder. The silicon powder is generally considered scrap, as it may be mixed with a variety of impurities, such as iron, water, polyethylene glycol and silicon carbide.
Because the silicon in the powder has such a high surface area, it is difficult to prevent contact with oxygen which then forms silicon dioxide. A vacuum or inert gas atmosphere has traditionally been utilized to help prevent such oxidation, but challenges remain. The vacuum pump may disturb the powder and if the silicon powder is melted, it requires expensive and elaborate processing steps to remove the high levels of contaminants.
The amount of silicon powder generated and ultimately discarded may be upwards of 45% of the original silicon amount handled. Current attempts at recycling the powder are typically expensive, do not reach the required purity for solar silicon, are time consuming and/or are not economically feasible.